Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants can include, among other things, gaseous compounds such as the oxides of nitrogen (NOx). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOx emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, some engine manufacturers have implemented a process called Selective Catalytic Reduction (SCR).
SCR is a process where a reductant (most commonly a urea/water solution) is injected into the exhaust gas stream of an engine and adsorbed onto a catalyst. The reductant reacts with NOx in the exhaust gas to form water (H2O) and elemental nitrogen (N2). Although SCR can be effective, when the reductant is sprayed onto relatively cool walls of the exhaust system it can condense. This condensation can create deposits that foul the injectors and cause premature wear and failure of the injection system. In addition, the condensed reductant may no longer be useful in reducing regulated emissions.
An exemplary reductant mixer is disclosed in U.S. Pat. No. 8,141,353 of Zheng et al. that issued on Mar. 27, 2012 (“the '353 patent”). Specifically, the '353 patent describes a system for treating exhaust gas by introducing an additive into the exhaust gas upstream from a catalyst. The system includes a mixer disposed between an additive injector and the catalyst. The mixer comprises a disc shaped wall structure having a plurality of perforated flow openings, and a cone shaped wall structure carrying a set of trapezoidal shaped mixer vanes that extend outward and intersect the disc shaped wall structure. The mixer vanes are formed by cutting a periphery of each vane to form an opening. The vane is then bent away from an upstream side of the mixer towards a downstream side of the mixer. An annular flange of the cone shaped wall structure engages an inner wall surface of an exhaust duct. The flow openings and mixer vanes together generate swirl in the exhaust that enhances mixing of injected additive with the exhaust.
While the mixer of the '353 patent may improve additive mixing, the mixer may still be less than optimal. In particular, the mixer of the '353 patent, because of its location downstream of the injector, does not inhibit the additive from being injected against a cool wall of the exhaust duct. In addition, the annular flange of the mixer may create an obstruction on which the injected additive can deposit. The swirl generated in the exhaust by the mixer may also be insufficient to adequately mix the exhaust. Further, the mixer may be intended for use with only a single additive injector and may not be applicable to systems having multiple injectors.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above and/or other problems of the prior art.